Here is a little project I did for some cute Halloween decor.
What you need:
As you can see, line the bottom with an inch of candy corn.
Next, line the side of the vase with your marshmallow peeps. Of course you can use a different type but I favored the ghosts here. I used just enough to go around the vase 1 time. which came out to about 3 rows. Then I used some sunflowers from the Dollar store, cut them to size and placed in the middle.
I have had this vase for about 3 years and no rotting or molding of any sort.